(PHP 4 >= 4.0.6, PHP 5)
mb_substr — Get part of string
Performs a multi-byte safe substr() operation based on number of characters. Position is counted from the beginning of str. First character's position is 0. Second character position is 1, and so on.
The string to extract the substring from.
Position of first character to use from str.
Maximum number of characters to use from str.
encoding 参数为字符编码。如果省略，则使用内部字符编码。
mb_substr() returns the portion of str specified by the start and length parameters.